Optical fibers tend to be very fragile and great care must be taken in handling them. This is particularly true of the glass fibers that provide the low loss and high quality transmissions required in communications applications. One technique used to protect optical fibers is to bundle several of them in a single cable. Such a cable may be a flat linear array of fibers held together by a web. Such a cable is known as a ribbon cable. Even greater protection is offered by spiral wound cables. In a spiral wound cable several fibers are bundled together and surrounded by filaments of a protective material such as an aramid fiber. The optical fibers and the protective material are retained by a spiral wrapping.
One problem with using such cables is that the fibers must fan out from the cable to reach their ultimate destinations. The area around such a fan out is subject to greater stresses that are other areas of the fiber. Such stresses could result in fiber breakage. In order to protect the fibers in the fan-out area, the fan out is often placed in a housing. The fibers enter the housing in the cable, are fanned out and exit in loose protective coverings. Some prior art fan-out modules simply bonded the incoming cables and the outgoing fibers, in their protective loose coverings, to the module at the entrance and the exit. This approach provides little protection against shock to the housing, as such shocks are transmitted to the fibers, and provides almost no strain relief for pulling forces on the cable or the fibers.
A second type of fan-out module embeds the entire interior of the module in a settable potting compound such as an epoxy. The fibers are thus held rigidly inside the housing. This provides somewhat better shock resistance and strain relief than the first type of fan-out module, but less than is desirable in a typical operating environment.